stream: rename `Duplex.toWeb()` type option to `readableType` #2936

Job	Run time
Build slim tarball	1m 31s
x86_64-linux: with shared libraries	2h 6m 24s
x86_64-darwin: with shared libraries	1h 21m 1s
aarch64-darwin: with shared libraries	1h 57m 12s
aarch64-linux: with shared libraries	1h 26m 56s
	6h 53m 4s

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